A scar on the seafloor
Southwest of Tasmania, the seafloor is torn by a colossal geological feature: the Tasman Fracture Zone. This immense crack is a transform fault, marking a section of the boundary between the Australian and Pacific tectonic plates. The zone plunges to depths of over 4,000 meters, creating sheer underwater cliffs that stretch for hundreds of kilometers. This dramatic topography is the result of immense tectonic forces, where plates grind past one another. The fracture zone is part of the larger Tasman Fracture Marine Park, which covers 42,501 square kilometers.
The park's depths range from the shallow coastal waters of 60 meters to an abyssal plain reaching 5,559 meters. This extreme variation in depth creates a complex variety of habitats, from sunlit surface waters to the crushing pressure and perpetual darkness of the abyss. The geology includes steep canyons, undersea mountains known as seamounts, and sections of a plateau over 400 kilometers long that rises three kilometers from the ocean floor. This structure is a result of the rifting between Australia and Antarctica, which began in the Late Cretaceous.
An isolated world of deep-sea life
The sheer walls and extreme depth of the Tasman Fracture Zone create a significant biogeographic barrier. This barrier isolates deep-sea populations, leading to the evolution of unique species. Research expeditions, such as those by the CSIRO vessel RV Investigator, have systematically mapped the seafloor and documented its inhabitants. These voyages use advanced tools like deep-tow camera systems to capture high-resolution images and video at depths approaching 2,000 meters.
Discoveries from these expeditions are extensive. Scientists have identified over 100 unnamed species, including new types of squat lobsters and hat maker crabs. The seamounts and ridges provide hard surfaces for deep-water corals, tulip-shaped glass sponges, and habitat-forming anemones and barnacles to grow. These coral communities, in turn, support a diverse range of other animals. Expeditions have recorded bioluminescent squid, ghost sharks, basketwork eels, and large aggregations of Orange Roughy (Hoplostethus atlanticus). The region is important for surface-dwelling animals, including 42 species of seabirds and several whale and dolphin species. The area around Mewstone, a rocky island within the park, is the world's largest breeding colony for the threatened shy albatross (Thalassarche cauta).